There has been increasing demand in the research reagent, diagnostic reagent, and chemical process industries for protein-based catalysts possessing novel capabilities. At present, this need is largely addressed using enzymes purified from a variety of cultivated microorganisms, generally members of the domains Bacteria and Archaea. However, because less than 1% of naturally occurring microorganisms have been grown in culture, alternative techniques must be developed to exploit the full-breadth of diversity for potentially valuable new products. We propose to develop a novel recombinant approach to generate and screen DNA libraries constructed from uncultured, mixed microbial populations. Because microorganisms can differ vastly in abundance in natural populations, a normalization strategy will be implemented. We predict that these normalized libraries will allow for greater screening efficiency and will result in the isolation of genes encoding novel biological catalysts.